U.S. Pat. No. 4,766,405 describes a fuel injector having a valve closing body connected to a valve needle and working together with a valve seat face designed on a valve seat body to form a sealing seat. For electromagnetic operation of the fuel injector, a solenoid works together with an armature connected in a friction-locked manner to the valve needle. An additional mass is provided in the form of a cylinder around the armature and the valve needle and is connected to the armature by an elastomer layer. One disadvantage is the complicated design featuring an additional component. The large-area elastomer ring is also a disadvantage for the variation of the magnetic field and makes it difficult for the field lines to close and thus interferes with achieving high attraction forces in the opening movement of the fuel injector.
U.S. Pat. No. 4,766,405 also describes an embodiment of a fuel injector; a cylindrical mass which is movably held and secured in position by two elastomer rings is provided around the armature and the valve needle for damping and reducing rebound. When the valve needle strikes the valve seat, this second mass can move relative to the armature and the valve needle and prevent rebounding of the valve needle. One disadvantage of the embodiment described there is the additional complexity and space required. The armature itself is not isolated and its momentum thus increases the tendency of the valve needle to rebound.
U.S. Pat. No. 5,299,776 describes a fuel injector having a valve needle and an armature which is movably guided on the valve needle and whose movement is limited by a first stop in the stroke direction of the valve needle and by a second stop against the stroke direction. Within certain limits, the axial movement play of the armature defined by the two stops results in isolation of the inert mass of the valve needle from the inert mass of the armature. This counteracts within certain limits the rebound of the valve needle from the valve seat face in closing of the fuel injector. However, since the axial position of the armature with respect to the valve needle is completely undefined due to the free mobility of the armature with respect to the valve needle, rebound pulses are prevented only to a limited extent. In particular, the design of the fuel injector known from U.S. Pat. No. 5,299,776 does not prevent the armature from striking the stop facing the valve closing body in the closing movement of the fuel injector and transmitting its momentum abruptly to the valve needle. This abrupt transfer of momentum can cause additional rebound pulses of the valve closing body.
It is also known from practice that the armature guided on the valve needle can be movably secured in its position by an elastomer ring. To do so, the armature is held between two stops, with an elastomer ring located between the armature and the bottom stop. However, then the problem arises that a bore through the armature is necessary to supply fuel to the valve seat face. The bore through the armature is provided close to the valve needle, and the valve seat side end of the bore is partially covered by the elastomer ring. This results in irregular pressure on the elastomer ring and finally the bore edges result in the destruction of the elastomer ring due to edge pressure. Furthermore, the vibrations are induced in the unsupported elastomer ring, which also contributes to destruction by the bore edges. This occurs especially at low temperatures, when the elastomer enters a rigid vitreous state.